1. Field of the Invention
The present invention relates to a motor and, in particular, to the structure of an armature for use in a motor.
2. Related Art
An armature core 11 for use in a motor, as shown in FIG. 11 (a), includes a plurality of salient poles 114 each of which is composed of a radially projecting arm portion 116 and a bow-shaped portion 117 spreading out on both sides at the leading end portion of the arm portion 116. An open slot 100 is formed between the mutually adjoining salient poles 114 and, using the open slot 100, a coil is wound around the arm portion 116 of each salient pole 114. For example, if the armature core 11 is rotated around a nozzle while guiding and drawing out a lead wire, then the lead wire can be wound around the arm portion 116 of the salient pole 114. In order to prevent the bow-shaped portion 117 from interfering with the movement of the nozzle in the present lead wire winding operation, there is secured a sufficiently wide opening width W as the open slot 100.
That is, in an operation to wind a drive coil 17, if, as shown in FIG. 11 (b), the opening width of the open slot 100 is too narrow, then the nozzle is not able to move to a sufficient degree, so that the drive coil 17 cannot be wound uniformly with respect to the arm portion 116 but the drive coil 17 is caused to cluster on the leading end side of the arm portion 116. As a result of this, there is produced a dead space D on the base end side of the arm portion 116; that is, not only the number of windings of the drive coil 17 is decreased in correspondence to the dead space D to thereby reduce the output of the motor, but also the windings of the drive coil 17 are caused to collapse, which results in the loosened drive coil 17.
Therefore, from the view point that the drive coil 17 should be wound properly, the opening width of the open slot 100 may be preferably increased to a large width but, in this case, there is raised a problem that the output characteristic of the motor is reduced by an amount corresponding to the increased width. That is, whether an armature 10 is rotated or a magnet is rotated, if the opening of the bow-shaped portion 117 is large, the magnetic flux collecting force of such opening portion is greatly decreased and the magnetic resistance thereof is greatly increased by an amount corresponding to the greatly decreased magnetic collecting force. As a result of this, the motor is caused to cog heavily, which interferes with the smooth and continuous rotation of the motor. As described above, in the conventional armature structure, the proper winding of the drive coil 17 and the smooth output of the motor provide an antinomic relation to each other that, if one of them is enhanced, then the other is worsened; that is, it is not possible to enhance both of them at the same time.
As a method for solving the above problem, in Japanese Patent Publication No. 63-157651 of Showa, there is disclosed an invention according to which a magnetic flux collecting plate (a magnetic flux collecting piece) is mounted on the outer peripheral surface of an armature core to thereby narrow the opening width of an open slot. However, with use of the disclosed invention, not only it takes time and labor to mount the magnetic flux collecting plate onto the armature core, but also the magnetic flux collecting plate cannot be extended any further in the axial direction thereof, which makes it impossible to enhance the motor output any further.